Pol Gen Somyos said police were still seeking nine other suspects in the same case.
Lt Gen Manas was an adviser to the Yingluck Shinawatra government and a classmate of former prime minister Thaksin Shinawatra at the Armed Forces Academies Preparatory School.
He is also accused of connections with “men in black” allegedly responsible for attacks on government forces during the 2010 political violence in Bangkok.